A clinic administrator taking down Knoxville's information shakes her head in disbelief. Within the hour, the co-creator and breakout star of MTV's cultishly beloved series "Jackass" — and a trio of spinoff movies that have a combined gross of more than $335 million — will be under general anesthesia and no longer able to rectify any self-inflicted finger fiascoes.

As a server at Blue Fin restaurant in Times Square, Amy Schumer — then an aspiring stand-up comic — said she waited on comedian Patton Oswalt every day for nearly a week, bringing him tea during each visit to help him combat his cold. They would strike up...